This application is based on and claims priority to Japanese Patent Application No. Hei 11-313035, filed Nov. 2, 1999, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
This invention relates to a fuel injection system for an engine, and more particularly to an apparatus and a method for controlling a fuel injection system of an engine.
2. Description of Related Art
In all fields of engine design, there is an increasing emphasis on obtaining more effective emission control, better fuel economy and, at the same time, increasing power output. This trend has resulted in the substitution of fuel injection systems for carburetors as the engine charge former.
Fuel injection systems typically inject fuel into an air intake passage(s) or directly into a combustion chamber(s). An ECU (electronic control unit) can control the fuel injection systems. The ECU typically controls an amount of the fuel. In some configurations, an engine speed sensor and a throttle valve position sensor are provided and respective signals from these sensors are used for determining suitable fuel amounts during operation of the engine. The fuel amounts can be defined in a control map stored in the control unit and can depend upon both engine speed and throttle valve position.
The signal from the throttle position sensor represents an amount of air or air flow rate introduced into the combustion chamber(s). The air amount, however, varies due to changes in the atmospheric pressure. For instance, the atmospheric pressure at higher elevations is lower than that at sea level. Thus, the air amount introduced into the air intake passage(s) at the higher elevations is inevitably smaller even though the throttle valve is placed in the same position. It is necessary therefore to adjust data relating to the air amount with data reflecting atmospheric pressure when effectively controlling fuel injection.
Conventional control systems may include an atmospheric pressure sensor. The control systems, however, are equipped with a number of other sensors for more accurate control of the engine. An intake pressure sensor is one of the sensors. This sensor senses an air intake pressure in the intake passage(s) during operation of the engine. Because the function of the intake pressure sensor is similar to that of the atmospheric pressure sensor, the intake pressure sensor can be used as the atmospheric pressure sensor. This is advantageous because at least one sensor, i.e., the atmospheric pressure sensor, can be omitted.
The idea is realized by providing a memory, for example, RAM, in the ECU to store a signal from the intake pressure sensor as an atmospheric pressure signal when the ECU starts operating but the engine stands still.
Additionally, many engines use a starter motor to crank or start themselves. The starter motor consumes a relatively large amount of power while cranking and hence a voltage supplied by the battery momentary falls during this period of time. FIG. 7 illustrates this situation. When the starter motor starts cranking, the battery voltage can abruptly drop to a level lower than a reset voltage of the ECU. The situation is likely to occur particularly when the engine is started under a cold condition. Once this happens, the ECU erroneously takes again the current intake pressure as the atmospheric pressure when it restarts operating. At this very moment, the intake pressure likely will be less than the actual atmospheric pressure because a negative pressure is generated due to the intake stroke of the engine. Accordingly, the injected fuel amount can deviate from the optimum amount and the engine operation can deteriorate. It is anticipated that this deviation will result in a leaner than desired mixture.
A need therefore exists for a fuel injection control that can hold an accurate atmospheric pressure during and after starting of the engine notwithstanding using an intake pressure sensor as an atmospheric pressure sensor.
In accordance with one aspect of the present invention, an internal combustion engine comprises a cylinder block defining at least one cylinder bore. A piston reciprocates within the cylinder bore. A cylinder head closes an end of the cylinder bore to define a combustion chamber together with the cylinder bore and the piston. An air induction system is arranged to introduce air to the combustion chamber. The air induction system includes an air intake passage. A throttle valve is moveably disposed within the air intake passage for admitting the air in proportion to an opening degree thereof. A first sensor is arranged to sense the opening degree to send out an opening degree data. A fuel injector is arranged to spray fuel toward the combustion chamber. A control unit is configured to determine an amount of the fuel at least based upon the opening degree data. A second sensor is primarily arranged to sense an intake pressure of the air flowing through the air intake passage to send out an intake pressure data. The second sensor is positioned downstream the throttle valve. The control unit adjusts the amount of the fuel based upon a reference data corresponding to an atmospheric pressure. The control unit includes a non-volatile memory for storing the intake pressure data as the reference data when the control unit starts operating and the engine stands still.
In accordance with another aspect of the present invention, an internal combustion engine comprises a cylinder block defining at least one cylinder bore. A piston reciprocates within the cylinder bore. A cylinder head closes an end of the cylinder bore to define a combustion chamber together with the cylinder bore and the piston. An air induction system is arranged to introduce air to the combustion chamber. The air induction system includes an air intake passage. A throttle valve is moveably disposed within the air intake passage for admitting the air in proportion to an opening degree thereof. A first sensor is arranged to sense the opening degree to send out an opening degree data. A fuel injector is arranged to spray fuel toward the combustion chamber. A control unit is configured to determine an amount of the fuel at least based upon the opening degree data. A second sensor is primarily arranged to sense an intake pressure of the air flowing through the air intake passage to send out an intake pressure data. The second sensor is positioned downstream the throttle valve. The control unit adjusts the amount of the fuel based upon a reference data corresponding to an atmospheric pressure. The control unit includes means for storing the intake pressure data as the reference data when the control unit starts operating and the engine stands still.
In accordance with a further aspect of the present invention, a control method is provided for an engine. The engine includes a fuel injector, an air intake passage having a throttle valve and a control unit having a non-volatile memory. The control method comprises sensing an air pressure in the intake passage under a standstill condition of the engine. Storing a data of the air pressure in the non-volatile memory is provided. Sensing an opening degree of the throttle valve under an operating condition of the engine is provided. Determining a first control data at least based upon a data of the opening degree is provided. Adjusting the first control data with a second control data corresponding to the data of the air pressure stored in the non-volatile memory is provided. Controlling the fuel injector based upon the adjusted first control data is provided.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiment which follows.